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Bone Densitometry. Interpretation of DEXA. Osteoporosis.

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Bone Densitometry


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    Presentation Transcript
    1. Bone Densitometry Interpretation of DEXA

    2. Osteoporosis • Osteoporosis is the most common metabolic bone disorder. It has been defined by the National Institutes of Health as an age-related disorder characterized by decreased bone mass and increased susceptibility to fractures in the absence of other recognizable causes of bone loss.

    3. Osteoporosis • Risk factors • may be superimposed upon either involutional or secondary osteoporosis, including : • Smoking • Alcohol • Poor diet • Lack of exercise • An early menopause • Strong family history • Small frame

    4. Osteoporosis • The normal rate of bone loss is 2% per year, hence 20-40% of the female bone mass is already lost by the age of 65 years of age, beginning before the menopause and accelerating afterwards

    5. Osteoporosis Osteoporosis progression over 2Y UC Steroids 59F

    6. Osteoporosis • Bone mass is the major determinant of bone strength that can be measured by non-invasive techniques, and accounts for 75-85% of this parameter

    7. Osteoporosis Measurement • Plain film, • Subjective, Radiogrammetry, Osteogram • SPA • DPA • DEXA • QCT • US • MRI

    8. Osteoporosis Measurement • Plain film, • Subjective, Radiogrammetry, Osteogram • SPA • DPA • DEXA • QCT • US • MRI

    9. Osteoporosis Measurement • Plain film, • Subjective, Radiogrammetry, Osteogram • SPA • DPA • DEXA • QCT • US • MRI

    10. Osteoporosis Measurement • Plain film, • Subjective, Radiogrammetry, Osteogram • SPA • DPA • DEXA • QCT • US • MRI

    11. Osteoporosis Measurement • Plain film, • Subjective, Radiogrammetry, Osteogram • SPA • DPA • DEXA • QCT • US • MRI

    12. DEXA DEXA has very high accuracy (the difference in the measurement from a known standard) and precision (observed deviation of serial measurements with time) both short and long term to within 1% at the hip and spine

    13. DEXA • DEXA is at present the most precise measurement of BMD • QCT is more sensitive to change

    14. DEXAInterpretation

    15. Find out as much relevant information as possible

    16. Find out as much relevant information as possible

    17. Bone DensitometryDEXA spine check list • Note the age, sex, ethnicity and weight • Does this match the reference ranges? • Is the bottom of L4 roughly at the level of the iliac crests • Are there any ribs on L1 • Scoliosis • Are the vertebrae correctly divided • Anything in the soft tissue

    18. Vertebroplasty

    19. Calcium Tablets

    20. Transitional vertebrae Wrong levels

    21. Bone DensitometryDEXA spine check list • Look for significant level to level variations • 15-20% difference between adjacent levels

    22. Bone Densitometry • In preventing Fxs it is the worst scenario that matters. • Generally a slight increase in density as descend the L spine. • Approx 6% increase between L1 and L4.

    23. What’s wrong with this scan? Divisions don’t account for scoliosis

    24. What’s wrong with this scan? Everything

    25. DEXA Femur check listHints for a good scan. • Patient should be straight on table. • Pack patient with rice bags. • Shaft of femur should be straight. • Rotate leg inward, this will hide the lesser trochanter.

    26. DEXA Femur check listHints for a good scan. • The Wards area is roughly half the neck area • Trochanteric area 8-14cm2 in women, 10-16cm2 in men • Check left and right and state side being used in report.

    27. Typical Femur Scan

    28. What’s wrong with this scan? Too much shaft

    29. What’s wrong with this scan? Insufficient tissue below neck

    30. What’s wrong with this scan? Set up for wrong leg

    31. What’s wrong with this scan? Includes ischium

    32. Bone DensitometryWHO uses T scores • Normal • > -1 SD below young adult • Osteopenia • -1 -2.5 SD • Osteoporosis • <-2.5 SD • Established (Manifest) Osteoporosis • + Fxs, usually spine, hip, proximal humerus, wrist, rib

    33. 007179 - Macro DEXA Template

    34. Bone Densitometry • Never round up figures • -1 is osteopenia, -0.99 is normal • -2.5 is osteoporosis, -2.49 is osteopenia

    35. Bone Densitometry 44F

    36. Bone Densitometry 44F

    37. Bone Densitometry 44F

    38. Bone Densitometry 44F

    39. Bone Densitometry • T score is compared to reference population, 20-45 years, same sex, any race, any weight. • Z score is matched for age, sex, weight and ethnicity.

    40. Two possible reasons for this lady’s Z score being worse than the T score?

    41. Two possible reasons for this lady’s Z score being worse than the T score? Obesity and race

    42. The T score is based on a white, same sex, age 20-40population. The patient's BMD is compared to this population's BMD.A lower T score means that the patient BMD is low compared to this young, healthy normal weight population. The Z score compares the patient to an adjusted population, it adjustsfor age, weight, and ethnic background. The Z score can be lower than the T score for the patient, if the average patient in this population has a higher BMD than the average in the T score population. This can be seen in patients with higher weights, (which increases bone density), and in African American groups, (which show increased bone density). If the patients comparison group has a generally higher bone density, then it is possible to have a poorer comparison to others of same age, than to younger comparisons in generally lower density group.

    43. 260 lb man, young Z above young T

    44. Black as Black Black as White

    45. Black as Black > Black as White T same Z up <

    46. Bone DensitometryWeight gain/loss and Z • Weight gain(or loss) will not affect Z score comparison, since Z scores are weight matched, but should cause an increase(or decrease) in absolute BMD. • An increase in weight, pushes up the reference range, and therefore the Z score may seem reduced, and vice versa. 2.2lbs=1Kg

    47. Bone DensitometryWeight gain/loss and T • Weight gain (or loss) should cause an increase(or decrease) in absolute BMD. • Weight gain (or loss) will affect T score comparison, since reference range will not have changed. • Hence an increase in weight with a corresponding increase in bone density, will look like a good improvement in T score, but fracture risk is unchanged.

    48. 51F 90Kg 53F 51Kg

    49. 1.172 1.176 SD = 0.1 Both between -2 and -3 SD below mean for age 1Y, 16lb gain, 5% BMD loss = significant increase in fracture risk

    50. Bone DensitometryComparison with previous • Are the studies comparable • Always compare like with like • Thornton L1-4 • 4th and Lewis (previously L2-4) • Any intervening events • Cannot compare Hologic and Lunar